1. Technical Field of the Invention
The present invention relates to a method for lubricating a two-cycle internal combustion engine, which is intended to prevent blow-by of an air-fuel mixture in a combustion chamber and hence to enhance fuel consumption and to purify exhaust gases. In particular, the present invention relates to a method for lubricating a two-cycle internal combustion engine of a type in which a control valve is disposed in a communicating passage for communicating a combustion chamber to a chamber portion adjacent to the combustion chamber, for controlling the opening/closing of the communicating passage. A fuel or an air-fuel mixture is injected or charged in the combustion chamber through the communicating passage and a highly compressed gas is injected or charged in the chamber portion through the communicating passage, which is intended to improve lubrication of a bearing portion of the control valve and lubrication of a sliding portion of a cylinder bore to a piston, and hence to enhance the maintenance performance and fuither improve fuel consumption.
2. Description of Background Art
In a related art two-cycle internal combustion engine, fuel supplied from a carburetor or the like is mixed with intake air, and the air-fuel mixture is sucked in a crank chamber and then supplied in a combustion chamber through scavenging openings. In this engine, since the timing of the opening of an exhaust opening is set to be earlier than the timing of the opening of the scavenging openings (an upper edge of the exhaust opening is higher than upper edges of the scavenging openings), there may easily occur exhaust of the air-fuel mixture supplied in the combustion engine into the exhaust opening, that is a so called blow-by of the air-fuel mixture.
The blow-by phenomenon is suppressed by an exhaust-pulsation effect. However, it is difficult to suppress the blow-by over the entire operational range. As a result, the blow-by exerts an adverse effect on fuel consumption and the purity of the exhaust.
Two-cycle internal combustion engines intended to solve such an inconvenience have been disclosed in Japanese Patent Laid-open Nos. Hei 3-1 318 and Hei 5-3 2521.
In the two-cycle internal combustion engine described in Japanese Patent Laid-open No. Hei 3-1 318, a high pressure chamber is connected to a crank chamber through a check valve; the high pressure chamber is connected to a combustion chamber through an air passage; and a solenoid valve is interposed at a lower end of the air passage. A fuel injection valve for injecting fuel in the combustion chamber is provided at an upper end of the air passage.
In the two-cycle internal combustion engine described in Japanese Patent Laid-open No. Hei 5-3 2521, a chamber portion is disposed adjacent to a crank case and a cylinder block. In addition, an intake control valve is interposed between a crank chamber and the chamber portion. A scavenging control valve is interposed between the chamber portion and a combustion chamber in a cylinder; and a fuel injection valve is provided for injecting fuel in the chamber portion.
The two-cycle internal combustion engine described in Japanese Patent Laid-open No. Hei 3-1 318 has a problem. Since the fuel supply opening is provided in a side wall of the cylinder at a position facing to the combustion chamber and, the fuel injection valve is disposed directly perpendicularly to the fuel supply opening, fuel spray collides with the cylinder wall on the exhaust opening side which is opposed to the fuel supply opening and thereby the fuel spray is liable to adhere on the cylinder wall.
When a fuel spraying timing occurs earlier in order to prevent interference between the piston and fuel spray, the fuel spray tends to be blown-by in the exhaust opening. In addition, when the fuel supply opening is disposed at a higher position to delay the fuel spraying timing, the fuel injection valve is directly exposed to a combustion gas at a high temperature, causing an inconvenience in that the injection valve needs a high thermal resistance.
The two-cycle internal combustion engine described in Japanese Patent Laid-open No. Hei 5-3 2521 has a problem. Since the air-fuel mixture injected from the scavenging control valve is supplied in the combustion chamber through all of the scavenging openings, the blow-by of the air-fuel mixture at the exhaust opening cannot be avoided.
To solve the problem of the related art engines, the present inventor has proposed a two-cycle internal combustion engine particularly in Japanese Patent Application No. Hei 8-269366. In the two-cycle internal combustion engine, a control valve is disposed in a communicating passage for communicating a combustion chamber to a chamber portion which is juxtaposed sideward of the combustion chamber and is continuous to a fuel injection device, for controlling opening/closing of the communicating passage, and fuel is injected or charged in the combustion chamber through the communicating passage and a highly compressed gas is injected or charged in the chamber portion through the communicating passage. With this configuration, since scavenging only by air is performed at the beginning of the scavenging step, it is possible to prevent a blow-by phenomenon of the air-fuel mixture in which the air-fuel mixture passes through the combustion chamber and is exhausted into an exhaust passage. Further, since fuel (rich air-fuel mixture) supplied in the combustion chamber becomes an air-fuel mixture at a suitable concentration in the combustion chamber, it is possible to obtain desirable combustion, and hence to achieve a high level fuel consumption and a high exhaust gas purifying performance.
The technique proposed by the present applicant, however, has a problem. Since lubrication of right and left bearing portions of the control valve is performed by enclosing oil in the bearing portions sealed by oil-seals in a state in which the right and left bearing portions are communicated to each other, a periodical maintenance is required to cope with degradation and consumption of the oil.
Further, in the technique proposed by the present inventor, lubrication of a sliding portion of a cylinder bore to a piston is performed by supplying oil from oil supply holes (see oil supply holes 66 in FIG. 5) provided in a cylinder wall surface on the exhaust opening side. However, there occurs a lack of lubrication at the sliding portion of the cylinder bore to the piston on the side of a rich air-fuel mixture supply polt facing to the combustion chamber and a highly compressed gas intake opening. This is because it is difficult to form a lubrication oil film on the sliding portion on the side of the above openings by the cleaning effect of the oil film due to the rich air-fuel mixture and the thermal effect of a compressed gas at a high temperature and a high pressure generated due to the explosion of the ignition.